The Stages of Fetal Development

As a baby grows in the womb, it undergoes many changes. While medical professionals tend to use 40 weeks of gestation as their reference, many people measure pregnancy in months. The stages of fetal development are three major divisions, which are conception, the embryonic period, and the fetal period.

Conception occurs around week two of gestation. This is due to the time that may transpire between the fertilization of the egg and the missed period. In this time lapse, the fertilized egg travels down the fallopian tube and into the uterus, implanting itself in the blood-rich uterine wall.

The next stage, the embryonic period, is the most critical time in fetal development, as the cells that will make up the placenta and those that will make up the baby divide and form, with all major systems are experiencing their foundational development. This stage lasts from week 2 till around week 11. By the sixth week, a heartbeat can be detected, and limbs begin to form.

At week eight, teeth begin to form under the gums, and intestines start to take shape. By the end of this stage, major organs will have begun to develop, as well as the central nervous system. Joints will have developed, as well as the first signs of the irises.

After the 11th week, the embryo is now called a fetus, and begins the last and longest of the stages of fetal development. From week 11 to 16, the fetus will develop genitals, hair, vocal chords, and even nails. Kidneys and the liver begin functioning, and bones start to harden.

From week 16 to 20, the fetus will undergo a major growth spurt, with fat developing under a thin skin. The fetus’s heart will pump 25 quarts of blood daily. Waste product begins accumulating in the bowel.

And the fetus will start to be awake and asleep for periods resembling that of a newborn, even hiccupping at times.

Development slows from weeks 21 to 24. By the end of this period, eyelids and eyebrows should be completely formed, and if a male, testes will start do descend. The fetus will weigh around 1.3 pounds by week 24.

In weeks 25 to 28, the baby continues to grow and develop. Ligaments form, and the nostrils open. The retinas form, and eyes can be completely opened. Lung development proceeds quickly during this period, in preparation for breathing air at birth.

A baby born at week 28 has a 90% chance of survival, though breathing would likely be an issue.

From week 29 till birth, nearly all fetal development is concentrated on the lungs. All the other major systems and organs are essentially complete.

The baby must also fatten up and develop immunities against the environment outside the shelter of the womb. By week 37, the baby’s weight will increase by about 1 ounce a day. Also by week 37, the pregnancy is considered to be full-term, and a baby delivered from this point on should have no developmental complications.